['ol Pinion head]

Extremely rare to find a "good" ratio (3.23 or 3.42) P series posi rear in the '65/66 Big OLDS.
Agree with Larry, that usage was only for a little while in big Olds. It's been near 15 years since I've run across a manual trans non AC '65 big Olds, & that was in a monster yard in MN that used to hold onto the old stuff much longer. That '66 had a 3.42 Safe-T-Track under it. Last Fall, two of us PY'ers were in another monster yard up north that had several '65 Olds Station wagons, the wagons are a good place to look. That long row of big Olds had other big Olds of that era setting on top of the wagons, along with trees & saplings growing between each car. No chance of getting any of the wagons jacked up.

On the 8.4" ring gear Type "O" Olds, have had quite a few 3.23-3.91 ratio Anti Spin 442 rears, & have gone though a few more for customers. The Type O's are a restoration piece, for any kind of strong performance, they lack the pinion support of the later 8.5 A-body. Always get a chuckle out of eBay listers noting the Type "O" A-body rears as "12 bolts", or as an OEM usage rear in Pontiac "GTO"s. Only Olds were originally built with Type "O" rears.